(1) Field of the Invention
The present invention relates to catalysts for hydrocarbon conversion. More particularly, the invention relates to pillared clay compositions with highly stable supergalleries.
(2) Description of Related Art
Pillared clay compositions are prepared by insertion of robust organic cations or inorganic polymeric hydroxy metal cations into the interlayers of clays to open the two adjacent 2:1 clay layers. Thereby unique internal micropore structures with large surface areas, pore volumes, intracrystal acidities, and catalytic activities are created. The larger the interlayer props used as pillars, the more surface areas and pore volumes became available for adsorption and catalytic reaction. Pillared clays should have excellent thermal and hydrothermal stabilities for practical application as catalysts. Under thermal and hydrothermal treatment the props should migrate from the interlayer galleries. The micropore structure with large surface areas, pore volumes, acidities, and catalytic activities needs to be retained. It is apparent that pillared clays with stable supergalleries are among the most useful catalytic materials available for catalyst adsorbents and catalyst carriers.
Up to now pillared clay compositions with highly stable supergalleries have not been reported in the literature. The item "supergallery pillared clays" has been applied to 2:1 layered derivatives in which the gallery height supported by the pillar is substantially larger than thickness of a host layer (.about.10 .ANG.). The "stable supergallery" means that the supergallery structure does not collapse under thermal and hydrothermal treatment below approximately 800.degree. C. The basal spacings D.sub.001) of the prior art pillared smectite clays were typically less than that of 30 .ANG.. Interlayer spacings (e.g. gallery heights) were typically no more than that of 20 .ANG.. For example, organic cation pillared smectites had basal spacings of less than 19.0 .ANG. corresponding to gallery heights of less than 9.4 .ANG. (Shabtaei et al., Proc. 6th Inter. Congr. Catal., B5, 1-7, 1976). Inorganic pillared smectites prepared by polymeric cationic hydroxy metal complexes containing aluminum, silicon or zirconium normally exhibited basal spacings of 18.0-22.0 .ANG.and interlayer spacings of 8.4-12.4 .ANG. (U.S. Pat. Nos. 4,176,090, 4,248,739, 4,367,163 and 4,757,040). Although the basal spacings of the pillared clay compositions have been improved in recent years, there was no general synthetic route to highly stable supergallery pillared clays. Chromium pillared smectites had a basal spacing of 27.6 .ANG. and interlayer spacing of 18.0 .ANG. (M. S. Zhou and T. J. Pinnavaia, Catalysis Today 2, 234-259 (1988)). Crystalline titanium pillared montmorillonites had a basal spacing of 29 .ANG. and interlayer spacing of.about.19 .ANG. (Yamanaka, S., et al., Mater. Chem. Phys. 17, 87 (1987)). Cerium pillared smectites prepared by developmental CeO.sub.2 sol had a basal spacing of approximately 30 .ANG. and an interlayer distance of.about.20 .ANG. (U.S. Pat. No. 4,637,992). A serious limitation of all the pillared clay compositions mentioned above were not Stable under thermal and, especially, hydrothermal treatment. The species that serve to prop open the adjacent 2:1 clay layer of smectites were expelled from the interlayer galleries and then caused the interlayer spacing to collapse during thermal or hydrothermal treatment. It is apparent that the disintegration of the pillar structure causes the micropore structure, adsorption performances, and catalytic activities to diminish drastically. As reported in the literature aluminum pillared smectites treated at 730.degree. C. for 4 hours with steam resulted in a loss of 90% of their surface areas and 80% of their pore volumes. Their catalytic activity for cracking gas oil drops sharply from 80% to 30% (Occelli, M. L., I & EC Prod. Res and Dev., 22, 553, (1983)).
So far the best previously reported pillared clay compositions with respect to stable galleries were aluminum pillared rectorites. These materials were prepared by reacting rectorite clays with polymeric aluminum chlorohydroxide solution. After steaming treatment at 800.degree. C. for 17 hours the aluminum pillared rictorites retained most of their gallery structure, adsorption performances, and catalytic activities. However, the products had a basal spacing of about 29.0 .ANG. corresponding to interlayer spacings of about 9.4 .ANG. due to a rectorite layer thickness of 19.6 .ANG.. Owing to the limited basal spacing of the prior pillared rictorites their surface areas, pore volumes, acidities, and catalytic activities were not good enough to meet requirements of the petroleum processing industry. For example a microspheric cracking catalyst containing the prior pillared rectorite compositions had a surface area of only 126 m.sup.2/ g, a pore volume of 0.13 ml/g, and a microactivity (MAT) of 58%. After steaming treatment at 800.degree. C. for 17 hours it has the MAT of 42% versus a commercial REY catalyst of 61%. In cracking heavy oil fraction (330.degree.-520.degree. C.) with a riser pilot plant the pillared rectorite gave a conversion of 63 versus commercial REY catalyst of 67 indicating that the activity of the prior pillared rectorite cracking catalyst is slightly lower than that of the REY zeolite cracking catalyst (Guan Jingjie et al., Proc. Intern. Cong. and exhib. on Pitrol. refining and Pitrol. Processing, Beijing, P. R. China, (1991)).
In the prior methods used for preparation of pillared clays, none were effective for obtaining derivatives with highly stable supergalleries. In general, unmodified polymerized aluminum chlorohydroxide solutions were used as pillaring reagents for the preparation of pillared clays. As reported in the literature, this pillaring agent has a characteristic .sup.27 Al NMR peak near 63.0 ppm, indicating a Keggin ion-like [Al.sub.13 O.sub.4 (OH).sub.24 (H.sub.2 O).sub.12].sup.+7, structure (abbreviated Al.sub.13). The Al.sub.13 species forms only single pillar structure. The typical structure model for pillared smectites prepared from Al.sub.13 is based on a single layer and single Al.sub.13 pillar aggregate (U.S. Pat. No. 4,176,090). The typical structure model for pillared rectorite prepared by reacting rectorites and Al.sub.13 is a double host layer and single pillar structure (U.S. Pat. No. 4,757,040). So the gallery heights of the pillared clays prepared from the Al.sub.13 oligomer are limited to 10 .ANG.. Although a method to enlarge the pore size by means of adding poly (vinyl alcohol) to clays was reported in the literature, it was not successful in obtaining stable supergallery networks. The pillared clays from this method lost their long range order when calcinated in the air. So pillared clay compositions with stable supergallery structure were not obtained (Kenzi Suzuki et al., Clay and Clay Mineral Vol. 36, No. 2 P147-152 (1988)).
All the data above clearly indicate that prior pillared clays lacked the desired stable supergallery structures needed to obtain highly catalytic activity for large molecular reactants. So far pillared clays with stable supergalleries and their preparation method have not been obtained in the prior art.